1. Field of the Invention.
This invention relates to the preparation of compositions by co-reacting a vanadyl alcoholate, an organic titanate and polyhydric alcohol compounds. More specifically, this invention relates to a process of preparing esters and polyesters in an improved manner by using theses novel compositions as esterification/transesterification catalysts.
2. Prior Art.
The preparation of esters and polyesters is well known in the art. These materials are prepared by esterifying mono- and/or polyhydric alcohols with mono- and/or polycarboxylic acids. In many instances it is desirable to prepare such esters or polyesters having a very low acid number, i.e., less than two, acid number being defined as the number of milligrams of KOH per gram of sample required to neutralize the acidity of the sample. However, the attainment of an ester or polyester having a low acid number is extremely difficult to achieve. For example, during the last stage of the esterification reaction, the reaction proceeds extremely slowly and hence in order to reduce the acid value it is necessary to heat for a lengthy period of time at relatively high temperatures. This, in many instances, tends to bring about formation of a darkened ester or polyester which is unsuitable for further use. Various attempts have been made to reduce the time of the esterification reaction. For instance, British Pat. No. 792,011 describes the use of iron, cadmium, cobalt, lead, zinc, antimony and manganese in the form of the metal, the metal oxide or the metal salt with a dibasic acid as catalysts which markedly reduce the esterification time. Organic titanium or organic zirconium compounds have been disclosed by U.S. Pat. No. 3,056,818 as being suitable as esterification catalysts. Titanium compounds are often insoluble in the product and must be removed by filtration or other tedious procedures. U.S. Pat. No. 3,716,670 teaches the use of a mixture of rhodium and vanadium compounds as catalysts for carboxylation or esterification. The technical literature also notes that esterification can also be effected by refluxing the acid and alcohol with a small amount of acid catalyst such as sulfuric acid, hydrochloric acid, and sulfonic acids or boron trifluoride. Acid catalysts of this type often cause undesirable side reactions resulting in color formation and must therefore be removed to insure a stable low acid number product.
Esters may also be prepared by a procedure known as a transesterification reaction. These transesterification reactions include the reaction between an ester and an alcohol to form a new ester and liberate an alcohol. Included also are the transesterification reactions where the components of the esters involved are polyhydroxy alcohols and polybasic acids. These reactions may, in some instances, be catalyzed by those substances which are employed for the esterification procedure. We have discovered that polyesters having an acid number less than two can be prepared in relatively short periods of time employing either esterification or transesterification procedures with the compositions of vanadyl alcholates, organic titanates and polyhydric alcohol compounds as catalysts.